Fire and intrusion detection are important for a myriad of reasons. Fire can cause serious damage to property and persons and can even result in loss of life to persons or animals caught in a fire. Additional damage beyond that caused by flames can be caused by smoke or soot or by water used to fight the fire. Such damage can result in significant financial losses—or worse—to the victims of a fire.
Intruders, whether human or animal, also can cause damage to persons or property, and so it may be desirable to detect and locate such intruders to avoid any problems resulting from their presence. In addition, in the case of a fire, it can be very important to know whether there are any persons in a burning location and where they so that fire fighters either can locate and rescue such persons or, if no one is present, do not need to take unnecessary risks to rescue persons who are not present.
Intrusion detection typically involves the emission of electromagnetic or sound waves and detecting their reflection from the intruder. Ultrasonic intrusion systems are described in, for example, U.S. Pat. No. 3,986,183 to Fujiwara and many others. Intrusion detection systems in which a microwave frequency is transmitted and an intruder detected due to reflections of the radiated energy are described in, for example, U.S. Pat. No. 5,576,972 to Harrison; U.S. Pat. No. 5,578,988 to Hoseit et al.; U.S. Pat. No. 5,793,288 to Peterson et al.; U.S. Pat. No. 5,796,353 to Whitehead; and U.S. Pat. No. 6,188,318 to Katz et al. The systems described in these patents all require an active emission of microwave radiation from a source, which is reflected by the object (e.g., an intruder) to be detected. For example, as described in the Harrison '972 patent, known objects or living entities may provide baseline signatures against which the reflected radiation can be measured. Movement of an intruder can be detected by use of the Doppler effect, i.e., by measuring a change in the reflected radiation as an object moves towards or away from the source of the radiation.
Fire protection engineering concentrates on the detection of both flaming and smoldering fire signatures, typically through the design of heat, smoke, and optical detectors and combinations of such detectors and arrays. Flame and radiation detectors can be used to monitor for the presence of sparks, burning embers and flames. Ultraviolet and infrared detectors can also be used to detect fire by sensing electromagnetic radiation at ultraviolet and infrared frequencies. Thermal sensing differentiates a temperature of an object from that of a predetermined steady state. For example, U.S. Pat. No. 6,724,467 to Billmers et al., describes a system and method for viewing objects at a fire scene by discriminating reflections from an object from smoke and fire. Some limited tests also have utilized acoustic sensors for fire detection.
Such techniques, however, are not infallible and frequently result in false alarms. For example, a thermal sensor in the proximity of a bathroom shower may detect rising air temperature from a hot shower and trigger an unnecessary alarm. In addition, since such thermal detectors do not detect smoke, they can be slower to react and detect a fire than are smoke detectors.
Consequently, thermal sensors are often used in combination with smoke detectors which operate upon the detection of particulate matter from smoke in the air. Particle and smoke detectors use photoelectric, ionization, carbon monoxide, gas-sensing, and photo beam technologies to sense byproducts of combustion. However, these devices also are not infallible, and may falsely trigger from, for example, cigarette or cigar smoke. Moreover, one or both of the thermal and smoke detectors may be slow to react to a growing fire, thus leading to greater risk to property or life. In addition, the presence of smoke can complicate the detection of fires. Studies show that 90% of wood smoke particles are smaller than 1 micron in size. Particles from oil smoke are in the 0.03 to 1 micron range, while particles from cooking smoke from grease are in the 0.01 to 1 micron size, as is tobacco smoke. Consequently, discrimination among types of smoke is difficult, which requires sophisticated pattern recognition algorithms and detector sensors to reduce the nuisance sensitivity (see L. A. Cestari, et al., “Advanced Fire Detection Algorithms using Data from the Home Smoke Detector Project,” Fire Safety Journal, 40 (2005), 1-28).
Microwave engineering technologies also have been considered as a means to detect flaming and smoldering fires, particularly when using multi-spectral electromagnetic wave sensing. The premise is that the fire's radiant heat transfer components generate a detectable signal in the microwave portion of the electromagnetic spectrum.
Electromagnetic waves are created when charged particles such as electrons change their speed or direction. These electromagnetic waves consist of an electric field and a magnetic field perpendicular to the electric field. The oscillations of these fields are reflected in the frequency and wavelength of the electromagnetic wave. The frequency is the number of waves (or cycles) per second. The energy of these waves may also be characterized in terms of the energy of photons, mass-less particles of energy traveling at the speed of light that may be emitted at certain discrete energy levels. The following mathematical relationship demonstrates a relationship among the wavelength of an electromagnetic wave, its frequency, and its energy:
      λ    =                  c        f            =              hc        E              where      λ    =          wavelength      ⁢                          ⁢              (        meters        )                  c    =          speed      ⁢                          ⁢      of      ⁢                          ⁢      light      ⁢                          ⁢              (                  3          ×                      10            8                    ⁢                                          ⁢          meters          ⁢                                          ⁢          per          ⁢                                          ⁢          second                )                  f    =          frequency      ⁢                          ⁢              (        Hertz        )                  h    =                  Plancks        '            ⁢      s      ⁢                          ⁢      constant      ⁢                          ⁢              (                  6.63          ×                      10                          -              27                                ⁢                                          ⁢          erg          ⁢                                          ⁢          s          ⁢                                          ⁢          per          ⁢                                          ⁢          second                )                  E    =          energy      ⁢                          ⁢      of      ⁢                          ⁢      the      ⁢                          ⁢      electromagnetic      ⁢                          ⁢      wave      ⁢                          ⁢              (                  erg          ⁢                                          ⁢          s                )            
Wavelength and frequency are the inverse of one another as related by the speed of light, and may be used interchangeably herein in the description of embodiments and the claims as equivalents of one another. Note that the energy of an electromagnetic wave is proportional to the frequency and is inversely proportional to the wavelength. Therefore, the higher the energy of the electromagnetic wave, the higher the frequency, and the shorter the wavelength.
The spectrum of electromagnetic waves is generally divided into regions or spectra, classified as to their wavelength or, inversely, as to their frequency. These bands of wavelengths (frequencies) range from short to long wavelengths (high to low frequency) and generally consist of gamma rays, x-rays, ultraviolet, visible light, infrared, microwave, and radio waves. The term “microwave” generally is used to refer to waves having frequencies between 300 Megahertz (MHz) (wavelength=1 m) and 300 Gigahertz GHz (wavelength=1 mm). Microwave radiation is highly directional, and the higher the frequency, the more directional the emitted radiation.
The radiation from electromagnetic waves can be emitted by thermal and non-thermal means, depending upon the effect of the temperature of the object emitting the energy. Non-thermal emission of radiation in general does not depend on the emitting object's temperature. The majority of the research into non-thermal emission concerns the acceleration of charged particles, most commonly electrons, within magnetic fields, a process referred to in the astrophysics field as synchrotron emission. For example, astrophysicists and radio astronomers look for synchrotron emissions from distant stars, supernovas, and molecular clouds.
On the other hand, thermal emission of radiation from electromagnetic waves depends only upon the temperature of the object emitting the radiation. Raising the temperature of an object causes atoms and molecules to move and collide at increasing speeds, thus increasing their accelerations. The acceleration of charged particles emits electromagnetic radiation which forms peaks within the wavelength spectrum. There may be a direct correlation in changes in temperature impacting the accelerations of the composite particles of an object with the frequency of the radiation and peaks within the spectrum. Once an object reaches its equilibrium temperature, it re-radiates energy at characteristic spectrum peaks.
Common forms of this radiation include blackbody radiation, free-free emission, and spectral line emission. A blackbody is a theoretical object that completely absorbs all of the radiation falling upon it and does not reflect any of the radiation. Thus, any radiation coming from a blackbody is from its inherent radiation and is not the result of any radiation incident upon it. Blackbody radiation is a basic form of thermal emission of electromagnetic radiation from an object whose temperature is above absolute zero (0 Kelvin). Practical examples of blackbody radiators include the sun and other stars in the galaxy.
Passive high-gain directional microwave antennas and receivers have been used to measure the temperature of a remote object in the technical field commonly known as microwave radiometry. Typical users of microwave radiometry are radio astronomers scanning extraterrestrial objects and the earth. A microwave radiometer known from the field of the astronomy sciences pointed at the sky can produce a measurable voltage output which is proportional to the temperature of the target. For example, the science of detecting the temperatures of planets is an established technology in the field of radio astronomy, and radio astronomers can use microwave apparatus to measure the temperatures of distant planets and stars. Orbiting satellites pointed back towards the earth may also use microwave apparatus to conduct remote sensing of regions of the earth's surface, for example, to detect volcanic activity or to take temperature readings generally.
Radio astronomy is internationally allocated certain bands of frequencies for research purposes according to the 1979 International Telecommunication Union's World Administrative Radio Conference, also known as “WARC-79,” (J. Cohen, et al., CRAF Handbook for Astronomy, Committee on Radio Astronomy Frequencies, European Science Foundation, 3d Ed. (2005)). These bands are free of microwave active transmission and so are relatively free of noise when used for passive detection, for example, from the stars or planets. Use of passive microwave frequencies at these internationally protected frequencies within the microwave radiation spectra may guarantee that reception is free of interference from active microwave radiation.
Some of the WARC-79 allocated bands are reserved as “PRIMARY exclusive.” These PRIMARY exclusive bands include 21.850 to 21.870 MHz, providing a 20 KHz wide band; 1.400 to 1.427 GHz, providing a 27 MHz band; 2.690 to 2.700 GHz, providing a 10 MHz band, 10.680 to 10.700 GHz, providing a 20 MHz band; 15.350 to 15.400 GHz, providing a 50 MHz band; and 23.600 to 24.000 GHz, providing a 400 MHz band. In addition, some bands are labeled as “PRIMARY exclusive” but are restricted according to region of the Earth's surface.
Other frequencies also are set aside and require “Notification of Use” when someone wishes to transmit on these frequencies. These frequencies include 4.950 to 4.990 GHz, providing a 40 MHz band. The 1.6 to 1.7 GHz band is utilized for missile tracking radar but the chances of interference in a passive fire detection system would be low. Still others are “PRIMARY shared with active.”
In any of these frequency bands, active microwave frequencies present in a passively received signal may be known to a passive receiver so that the active frequency can be distinguished and ignored. For example, 1.400 to 1.427 GHz provides a protected bandwidth of 27 MHz. A wider band may be received at an antenna and block converted. Alternatively, the output can be narrowed by a bandpass filter. Also, conventional low noise amplifiers may pass a band of interest and provide gain as will be further discussed herein. In addition, passive microwave reception at this frequency range may be combined with reception of microwave radiation at other microwave frequencies outside this range, and known anomalies or other noise interference can be filtered or discriminated using conventional processes from the resulting signal. Moreover, other microwave frequencies including or overlapping the internationally protected bands may be detected over wider bandwidths such as 100 MHz to several GHz.
Improved devices for microwave detection include, for example, use of metal-semiconductor field effect transistors (MESFETs) for low noise block converters. Such microwave detection devices are described in several United States patents, including U.S. Pat. No. 7,052,176 to Stephan et al.; U.S. Pat. No. 5,302,024 to Blum; U.S. Pat. No. 5,370,458 to Goff; and U.S. Pat. No. 6,767,129 to Lee et al. Devices for microwave detection are presently less expensive when detecting radiation in a range of microwave frequencies less than 25 GHz; however, improvements in microwave detection circuitry to practical application at higher frequencies up to the infrared region should not be taken to limit embodiments described herein.
Other technical fields using detection of electromagnetic radiation in the microwave frequency range include the technical field of cellular telecommunications. Typical cellular frequencies include 800 MHz and 1.8 GHz. Intermediate frequency may be at 70 or 140 MHz. In the cellular telecommunications field, it is conventional to provide an antenna pole or mount on a building or other fixed structure having some height. For example, FIG. 8 of U.S. Pat. No. 5,724,666 to Dent shows a plurality of antenna arrays 210, 212, each having respective amplifiers 216, wherein each array appears as a plurality of directional elements 224 which may be used for transmitting and receiving.
The use of passive microwave detection in the field of radio astronomy is described in several U.S. patents, including U.S. Pat. No. 4,499,470 to Stacey; U.S. Pat. No. 4,645,358 to Blume; U.S. Pat. No. 5,526,676 to Solheim et al.; and U.S. Pat. No. 6,729,756 to Sezai. The '470 patent to Stacey describes a satellite over the oceans of the Earth, their mapping as the satellite passes between land and water and monitoring of the temperature of the ocean below. The '358 patent to Blume describes a problem in the radio astronomy field that measurement of the Earth's surface properties and those of the universe can be very inaccurate, especially in cases of low contrast with the background and describes a Raleigh-Jeans approximation procedure for overcoming such problems. The '676 patent to Solheim et al. describes principles of microwave radiometry especially applicable to detection of water vapor and cloud masses using frequencies, for example, at 50-70 GHz, 19-29 GHz and 40-80 GHz. The '756 patent to Sezai discusses use of a deep space reference temperature of 2.70 Kelvin as well as a hot calibration source.
The principles of radio astronomy also have been applied to measuring energy inside a human body. Such use can be seen in, for example, U.S. Pat. No. 4,416,552 to Hessemer, Jr. et al.; U.S. Pat. No. 4,532,932 to Batty, Jr. (tumor cells); U.S. Pat. No. 4,583,869 to Chive et al. (use of two probes); U.S. Pat. No. 4,605,012 to Ringeisen et al. (hyperthermia); U.S. Pat. No. 5,677,988 to Takami et al. (internal temperature of human body); U.S. Pat. Nos. 4,715,727 and 6,932,776 to Carr (heating at 915 MHz and measuring at 4.7 GHz); U.S. Pat. No. 4,798,209 to Klingenbeck et al. (diseased human tissue); U.S. Pat. Nos. 5,176,146 to Chive and 5,688,050 to Sterzer et al. (mammography); U.S. Pat. No. 6,543,933 to Stergiopoulos et al. (the skull); and U.S. Pat. No. 6,773,159 to Kim et al., U.S. Pat. No. 7,121,719 to Lee et al. and U.S. Pat. No. 7,197,356 to Carr (microwave catheter).
Microwave engineering technologies have also been investigated for use in detecting flaming and smoldering fires. In research by the inventors, fire has been demonstrated to actually be “plasma,” a phenomenon often referred to as the fourth state of matter. Plasma is an ionized gas that consists of a mixture of electrons (negatively charged particles) and ions (atoms that have lost electrons, resulting in a positive electric charge). Fire can be easily classified as plasma, because it often behaves like a gas, can conduct electricity, and is affected by magnetic fields. Common examples of a plasma fires range from the Sun to the arc formed during electric arc welding, both of which can offer a broad electromagnetic spectrum of radio interference.
Detection of fires by microwave engineering techniques relies upon the fact that thermal radiation from fires generates a detectable signal in the microwave portion of the electromagnetic spectrum which, like the microwave radiometer, can create a measurable change in voltage output which is proportional to a temperature.
For example, one use of microwave technologies in the field of fire detection appears in a 1995 National Institute of Standards and Technology (NIST) report by Grosshandler entitled, “A Review of Measurements and Candidate Signatures for Early Fire Detection,” NISTIR 5555, January, 1995 at pp. 13-14. The NIST report suggests that the concept of multi-spectral electromagnetic wave sensing may be applicable to fire detection. The report cites a “modified microwave motion detector . . . for monitoring the presence of a flame within a multi-burner natural gas furnace,” citing Berman et al. (1992). (C. H. Bermann et al., “Microwave Backscattering Fuel/Air Ratio Control and Flame Monitoring Device,” Fossil Fuel Consumption, American Society of Mechanical Engineers, Vol. 39, Book G00645, 1992). According to U.S. Pat. No. 5,785,426 to Woskov et al., a waveguide may be disposed within a furnace to direct radiation through a window to a heterodyne receiver disposed outside the furnace; this radiation can be used to measure furnace temperatures where the microwave radiation is in the range of 130-140 GHz and converted to 0.4-1.5 GHz for detection. U.S. Pat. No. 5,829,877 to Baath describes utilizing microwave energy and, as shown in FIG. 5 of Baath, describes detecting certain relevant peaks, for example, SO2, NO2, H2O, and NH3, among other compounds known as products of combustion.
A German 2001 NIST paper suggests that Daimler Chrysler Aerospace AG conducted earlier experiments in fire detection using microwave energy (T. Kaiser et al., “Is Microwave Radiation Useful for Fire Detection?” Proceedings of the 12th International Conference on Automatic Fire Detection, AUBE'01, Volume 965, Mar. 26-28, 2001, Gaithersburg, Md., NIST Special Publication). The purpose of these experiments, which is not further explained, was to detect fires in garbage bunkers. The possibility of using microwave engineering technologies in passive fire detection is also described in the NIST Conference paper in 2001 by Kaiser et al. which further describes the use of microwaves to passively detect a fire using a conventional Dicke switch operated at 1 KHz to compare a reference temperature of a room wall with measurements at 11 GHz in the microwave region and a bandwidth of 1 GHz. (See R. H. Dicke, “The measurement of thermal radiation at microwave frequencies,” Rev. Sci. Instr. Vol. 17, pp. 268-275, 1946). The discussed technique relies upon thermal radiation from fires generating a detectable signal in the microwave portion of the electromagnetic spectrum. To do so, Kaiser et al. further suggest use of a commercial satellite dish and a superheterodyne low noise converter to measure the microwave radiation of a target test fire.
Follow-up tests are described by Kempka et al. in 2006, and expand the frequency range of the initial Kaiser et al. experiments from 2 to 40 GHz (T. Kempka et al., “Microwaves in Fire Detection,” Fire Safety Journal, Volume 41, 2006, pp. 327-333). According to this 2006 publication, thermal radiation may be measurable utilizing four broadband antennas to cover four separate frequency bands of operation, i.e., 2-12, 12-18, 18-26, and 26-40 GHz bands of operation and respective bandwidths at 100 MHz each. “For each configuration one sample will be measured in the first frequency band. Then the receiver changes to the next frequency band and takes another sample. After all the selected frequency bands are measured, the receiver will measure the first band again.” Kaiser et al. further suggest using a “hot load” having a temperature of 100° C. (373 K) to calibrate their apparatus at a reference temperature. Certain fires were detected 90 seconds after ignition while another type of fire was detected 80 seconds after a heater was switched on. The time difference between samples was about 3.5 seconds.
Significant tests conducted by the inventors have expanded the initial reported results, have demonstrated methods to reduce interference by use of selected frequencies and isolation of spurious electromagnetic noise, and have introduced new concepts beyond fire detection to intrusion and security alerting. The inventors have presented and published their research findings based on these and other tests at the 2007 Interflam international engineering meeting and symposium (D. J. Icove and C. Lyster, “Microwave Fire Detection: A Survey and Assessment,” Interflam2007, University of London).
There are a broad range of examples that demonstrate a long-felt need where microwave fire and intrusion technologies can play an important role, particularly when such a system is fully automated.
For example, in broad surveillance to guard against forest fires, many of which can quickly burn valuable timber and threaten human life, microwave early detection technology would be of extreme benefit. Due to the geometric growth of uncontained forest fires, proactive early detection is highly desired so that a fire can be rapidly and aggressively extinguished before it becomes uncontrollable.
The military also could use microwave fire and intrusion technologies in their support and security efforts, for example, to monitor and protect battlefields, bridges, harbors, international crossing points, and other critical infrastructures. Another benefit of these technologies is that it can passively detect aircraft coming over the horizon at any altitude.
In addition, domestic farming activities could benefit from microwave fire and intrusion detection. Since the technique is also sensitive to body temperatures within the field of view of the receiving antennae, the tracking and corralling of livestock such as cattle over ranges, entering corrals, and even wandering outside boundaries could be beneficial, particularly for those in the milking industry. This technology could also determine thermal signatures of livestock, humans, or predators so that such animals can be monitored and undesired intruders identified.
Microwave fire and intrusion detection capabilities can also be used to detect the movement of vehicles along roads and tunnels and shipboard movements along channels. Signature analysis could identify the traffic flow and thermal signatures differentiating between cars, trucks, motorcycles, and other vessels. This technique could also identify stalled vehicles or those catching fire particularly in high density underground tunnels.
These and other uses can be made of a microwave fire and intrusion detection method and apparatus in accordance with aspects and features discussed below.